The present invention relates to data storage systems. More specifically, the present invention relates to data storage systems using read heads which utilize the giant magnetoresistive (GMR) effect.
Magnetic sensors utilizing the GMR effect, frequently referred to as xe2x80x9cspin valvexe2x80x9d sensors, are known in the art. A spin valve sensor is typically a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the xe2x80x9cpinned layerxe2x80x9d because it is magnetically pinned or oriented in a fixed and unchanging direction by an adjacent anti-ferromagnetic layer, commonly referred to as the xe2x80x9cpinning layer,xe2x80x9d through anti-ferromagnetic exchange coupling. The other ferromagnetic layer is called the xe2x80x9cfreexe2x80x9d or xe2x80x9cunpinnedxe2x80x9d layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields.
In a giant magnetoresistive sensor, a sense current is applied to the sensor. In the presence of a magnetic field such as that provided by magnetic storage medium, the resistance of the sensor changes resulting in a change in voltage due to the applied sense current. This voltage change may be measured and used to read back information. The operation of one configuration of a GMR sensor is described in U.S. Pat. No. 4,949,039, issued Aug. 14, 1990 to Grxc3xcnberg, entitled xe2x80x9cMAGNETIC FIELD SENSOR WITH FERROMAGNETIC THIN LAYERS HAVING MAGNETICALLY ANTIPARALLEL POLARIZED COMPONENTSxe2x80x9d.
GMR based sensors provide a greater response to a magnetic field in comparison to non-GMR type MR sensors (called anisotropic magnetoresistive (AMR) sensors) in which the resistance of the material changes with applied magnetic field. Thus, GMR sensors are the preferred type of magnetoresistive sensor. One type of sensor which utilizes both GMR and AMR effects is described in U.S. Pat. No. 5,206,590 issued Apr. 27, 1993 to Dieny et al. and entitled xe2x80x9cMAGNETORESISTIVE SENSOR BASED ON THE SPIN VALVE EFFECTxe2x80x9d. In the Dieny et al. patent, the magnetization vector in the pinned layer is fixed perpendicular to the air bearing surface (ABS) of the slider and the magnetization vector of the free layer is parallel to the ABS. Further, the field to be detected is along the hard axis of the free layer. FIG. 9 of Dieny et al. shows that the excitation field Ha is perpendicular to the easy axis magnetization direction and to the ABS. This is similar to the configuration in U.S. Pat. No. 5,739,988 to Gill in which the sense current is oriented at an angle of 45xc2x0 relative to the ABS.
As storage density increases, the magnetic field being sensed during the readback becomes smaller. Therefore, there is an ongoing desire to provide improved sensitivity of read heads for data storage systems.
A data storage system includes a storage medium having a data surface with data stored thereon, the stored data comprises variations in magnetic fields across the data surface. A slider is adapted to move across the data surface, the slider includes an air bearing surface which is substantially parallel to the data surface. A current source provides a sense current (I) and readback circuitry is adapted to receive a readback signal and responsively provide a data output. A magnetoresistive sensor carried on the slider is adapted to receive the sense current (I) in a sense current direction through the sensor, readback data from the data surface in response to variations in the magnetic field across the disc surface, and responsively provide the readback signal to the readback circuitry. The sensor is adapted to exhibit a GMR effect in response to a magnetic field. The sensor includes a free layer and a pinned layer. The free layer further provides an anisotropic magnetoresistive (AMR) response to the magnetic field. The quiescent bias point of the magnetization vector of the free layer (MFREE) includes a component which is perpendicular to the sense current direction to thereby enhance the sensitivity of the AMR response such that the readback signal is a function of the GMR effect and the AMR response of the sensor.